This invention relates generally to diesel engines that power automotive vehicles such as trucks. In particular it relates to a system and method for improving the response of a high-pressure oil pump that delivers oil to a rail that serves engine fuel injectors.
A high-pressure pump that delivers high-pressure oil for the operation of certain devices on a diesel engine, such as fuel injectors, may be driven directly by the engine. For example, the high-pressure oil may be delivered to a rail that serves the fuel injectors. The pressure in the rail, and hence pump pressure is regulated by relieving pump oil to a sump. The relieved oil serves no particular purpose, and hence may be considered a necessary inefficiency in operating the engine.
An alternative that is the subject of inventive activity involves using a throttled inlet pump. Such a pump does not spill high-pressure oil to the sump because the pressure at the pump outlet, and hence pressure in the rail, are controlled by selectively throttling the pump inlet. The pump inlet through which oil is drawn from the sump comprises a variable throttle that is electrically controlled to selectively throttle the oil entering the pump so as to cause the pump to deliver oil at a desired regulated pressure without spilling to the sump.
Different engine operating conditions call for the development of different pump outlet pressures, and so an ability to change pressure by electric control of the pump inlet throttle is desirable. While this throttled inlet pump is capable of producing a variable pump outlet pressure in conjunction with improved operating efficiency, certain aspects of engine operation may require that pump outlet pressure be changed especially quickly and with accuracy. Because the pump is being driven directly by the engine, engine speed change may also be a factor in pump operation.
A modern diesel engine also comprises an electronic control that is processor-based and processes certain data to develop data used in control of various aspects of engine operation. Such a control can control operation of a throttled inlet oil pump.
It was discovered that a certain throttled inlet pump under development for use with a diesel engine because of certain desirable attributes was unable to achieve desired response to changes in processed data calling for change in pump outlet pressure.
The present invention relates to a solution that is embodied in control strategy for the pump, rather than a solution involving modification of the pump design. The inventive solution has obvious advantages because it can be embodied in software that is programmable.
One aspect of the present invention relates to a control for a throttled inlet oil pump to control oil pressure in a rail that serves injectors of a diesel engine. The control comprises a processor that processes certain data to develop data for selectively restricting a throttle at the pump inlet. The processor processes data to develop error data defining error between a desired injector control pressure in the rail and actual injector control pressure in the rail. The processor further comprises offset data values correlated with values of the error data and adds a correlated offset data value to a prevailing value of error data to introduce an offset into the prevailing error data value. This creates an offset error data value. The processor further processes the offset error data value to create a value for the data that establishes the extent of throttle restriction.
Another aspect of the present invention relates to a strategy for control for a throttled inlet oil pump as described above.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. The disclosure includes accompanying drawings, briefly described as follows.